In the manufacture of integrated circuits (IC's), integrated circuit packaging, IC wafers and multi-chip modules, it is necessary to test the circuits as part of the manufacturing process. The testing is performed by creating a temporary electrical contact between a test probe or probes with selected points on the circuit under test. A predetermined programmed test is then undertaken utilizing signals applied to the circuit and derived therefrom through the probes. As development of circuits and circuit manufacturing technique has progressed, the number of required probe contacts has substantially increased and the frequencies at which the circuits are tested has increased. The combination of high probe numbers and high frequency subjects the probe card and probe design to significant limitations.
One of the techniques for mounting test probes is the utilization of an epoxy ring-style probe card constructed in a manner similar to printed circuit boards and incorporating an opening surrounded by probes depending from the card or board. The circuit under test is then raised into contact with the depending probes with the individual probes contacting predetermined contact pads on the circuit to be tested. The mounting of the probes on the probe card and the interconnection of such probes to contact pads or points on the probe card to permit the probes to be connected to test circuitry has resulted in numerous prior art design concepts.
The high frequency used for such probing limits the applicability of epoxy ring-style probe cards since such probe cards typically incorporate uncontrolled impedance paths, possibly as long as several inches, on the probe card. Wire probes, with lumped parasitic inductance of up to 20nH severely degrades signal fidelity above 50MHz due to cross-talk and signal attenuation.